1. Field of the Invention
This invention relates to a semiconductor-encapsulating epoxy resin composition having excellent moldability and reliability and a good solder dipping stability.
2. Description of the Related Art
Epoxy resins have an excellent heat resistance, moisture resistance, and electrical characteristics, and various characteristics can be obtained by modifying the recipes thereof. Accordingly, therefore, epoxy resins are used as for paints, adhesives, and industrial materials such as electrically insulating materials.
As methods of encapsulating electronic circuit parts such as semiconductor devices, a hermetic encapsulating method using metals or ceramics, and a resin encapsulating method using a phenolic resin, a silicone resin, an epoxy resin or the like have been proposed, but from the economical viewpoint, the productivity and the balance among physical properties, the resin encapsulating method using an epoxy resin is mainly adopted.
According to the encapsulating method using an epoxy resin, a composition formed by adding a curing agent, a filler and the like is used, and a semiconductor element is set in a mold and is usually encapsulated by the transfer molding method or the like.
The main characteristics required for the encapsulating epoxy resin composition are reliability and moldability. The moisture resistance is included by the term reliability, and the flowability, hot hardness and flash-preventing property are included by the term moldability.
When a resin-encapsulated semiconductor is allowed to stand in a high-temperature and high-humidity environment, water seeps through the encapsulating resin or the interface between the encapsulating resin and a lead frame to cause defects in the semiconductor. Accordingly, the term moisture resistance as used herein refers to the property of preventing or minimizing the above-mentioned imperfections of the semiconductor caused by water. Note the recent increases in the degree of integration of semiconductors has led to a demand for a higher moisture resistance.
Usually, a silane coupling agent is added, to improve the moisture resistance of an encapsulating resin. More specifically the addition of an epoxysilane (Japanese Examined Patent Publication No. 62-18565), the addition of a mercaptosilane (Japanese Unexamined Patent Publication No. 55-153357), and the addition of an aminosilane having a primary amino group (Japanese Unexamined Patent Publication No. 57-155753) have been proposed.
The addition of a silane coupling agent to a sealing resin effectively improve the moisture resistance, but it has been found that a higher moisture resistance is required for a semiconductor having a high degree of integration and the moisture resistance provided by the conventional silane coupling agents is still too low.
In the conventional method of adding an aminosilane having a primary amino group, the moisture resistance is improved, and simultaneously, moldability-improving effects such as an improvement of the hot hardness and reduction of the formation of flash are obtained. Nevertheless, this method cannot be practically adopted because the flowability is reduced.
In the field of semiconductor integrated circuits, techniques of increasing the integration degree and reliability recently have been developed, and the automation of the step of assembling semiconductor devices has been advanced.
To attach a semiconductor device of the flat package type to a circuit board, a method has been adopted in which soldering of every lead pin is carried out, but currently a surface mounting method is employed in which a semiconductor device is entirely dipped in a solder bath heated to a temperature higher than 250.degree. C. to effect soldering. Accordingly, in a conventional package encapsulated by an encapsulating resin, cracking of the resin portion occurs at the soldering step, whereby the reliability is lost, and accordingly, the obtained product cannot be practically used.
Various methods of improving the solder cracking resistance of encapsulating resins have been examined. For example, a method of using a biphenyl type epoxy resin has been proposed (Japanese Unexamined Patent Publication No. 63-251419). This method of using a biphenyl type epoxy resin improves the solder cracking resistance of the encapsulating resin, but the moisture resistance is lowered, the hot hardness at the molding is, low and the formation of flash is heightened.